Adhesive for polarizing plate, polarizing plate, manufacturing method therefor, optical film and image display

ABSTRACT

An adhesive of the invention is used for polarizing plate to provide a transparent protective film on at least one side of a polarizer and comprises a resin solution comprising a polyvinyl alcohol-based resin, a crosslinking agent and a colloidal metal compound with an average particle size of 1 nm to 100 nm, wherein 200 parts by weight or less of the colloidal metal compound is added to 100 parts by weight of the polyvinyl alcohol-based resin. The adhesive for polarizing plate can reduce the occurrence of knicks.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an adhesive for polarizing plate. Theinvention further relates to a polarizing plate and manufacturing methodthereof using the adhesive for polarizing plate. The polarizing platealone or an optical film obtained by laminating the polarizing plate canconstitute an image display such as a liquid crystal display, an organicEL display or PDP.

2. Description of the Related Art

In the liquid crystal displays, for example, it is indispensable todispose polarizers on both sides of a glass substrate providing asurface of a liquid crystal panel according to an image formation schemeadopted in the display. A polarizer is generally obtained in a procedurein which a polyvinyl alcohol-based film is dyed with a dichroic materialsuch as iodine, thereafter, the film is crosslinked with a crosslinkingagent and then, mono-axially stretched to thereby form a film. Since thepolarizer is manufactured by stretching, it is easy to shrink. Since apolyvinyl alcohol-based film comprises a hydrophilic polymer, the filmis very easily deformed especially in a humidified condition. Since thefilm itself is weak in mechanical strength, there has been a problemthat the film is torn. Hence, adopted is a reinforced polarizing platemanufactured in a procedure in which a transparent protective film ortransparent protective films each made from triacetyl cellulose or thelike are adhered to on one side or both sides of a polarizer. Thepolarizing plate is manufactured by adhere the transparent protectivefilm onto a polarizer using an adhesive.

In recent years, the range of uses of liquid crystal displays has beenincreased and extended to cover from portable terminals to large screenhome TVs, and their standards have been defined for each application. Inparticular, portable terminal applications, which must be portable forusers, strongly demand durability. For example, polarizing plates arerequired to have water resistance to such an extent that theirproperties and form will not change even under humidified conditionssuch as conditions causing dew condensation.

As mentioned above, a polarizer may be reinforced in strength with atransparent protective film to form a polarizing plate before use. As anadhesive for polarizing plate used in adhesion of the polarizer and thetransparent protective film to each other, an aqueous type adhesive isconventionally preferable and, for example, a polyvinyl alcohol-basedadhesive obtained by mixing a crosslinking agent into a polyvinylalcohol aqueous solution has been employed. A polyvinyl alcohol-basedadhesive may cause peeling at the interface between a polarizer and atransparent protective film in a humidified environment. This isconsidered because a polyvinyl alcohol-based resin, which is a maincomponent of the adhesive, is a water-soluble polymer and a possibilityof dissolution of an adhesive occurs in a situation of dewing. In orderto cope with the problem, a proposal has been offered of an adhesive forpolarizing plate containing a polyvinyl alcohol-based resin having anacetoacetyl group, and a crosslinking agent (see, for example, JapaneseUnexamined Patent Publication (JP A) No. 7-198945).

The preparation of polarizing plates has a problem in which knicks(knick defects) can occur when a polarizer is bonded to a transparentprotective film with the above-mentioned polyvinyl alcohol-basedadhesive interposed therebetween. Knicks are defects of localirregularities formed at the interface between the polarizer and thetransparent protective film. Against such knicks, there is proposed amethod that includes using, as a polarizer, a polyvinyl alcohol filmwith a controlled water content and with its surface treated with acalendar roll under specific conditions, and laminating the film and atransparent protective film (see JP-A No. 10-166519. Knicks areparticularly easy to occur when a polyvinyl alcohol-based resin havingan acetoacetyl group is used for the polyvinyl alcohol-based adhesive.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an adhesive for polarizingplate which can reduce the occurrence of knicks.

It is another object of the invention to provide a polarizing plateusing the adhesive for polarizing plate and a manufacturing methodthereof. It is yet another object of the invention to provide an opticalfilm laminating the polarizing plate, further another object of theinvention to provide an image display such as a liquid crystal displayusing the polarizing plate or the optical film.

The inventors have conducted serious studies in order to solve the abovetasks with findings that the objects can be achieved with an adhesivefor polarizing plate shown below, having led to completion of theinvention.

The present invention relates to an adhesive for polarizing plate usedfor providing a transparent protective film on at least one side of apolarizer, comprising: a resin solution comprising a polyvinylalcohol-based resin, a crosslinking agent and a colloidal metal compoundwith an average particle size of 1 nm to 100 nm, wherein 200 parts byweight or less of the colloidal metal compound is added to 100 parts byweight of the polyvinyl alcohol-based resin.

The adhesive for polarizing plate of the invention contains not only apolyvinyl alcohol-based resin and a crosslinking agent but also acolloidal metal compound with an average particle size of 1 to 100 nm.The occurrence of knicks is reduced by the action of the colloidal metalcompound, so that the yield of the production of polarizing plates canbe increased, and thus the productivity of polarizing plates can beimproved.

In the adhesive for polarizing plate, as the colloidal metal compound,at least one selected from the group consisting of colloidal alumina,colloidal silica, colloidal zirconia, colloidal titania, and colloidaltin oxide, is preferably used.

In the adhesive for polarizing plate, the colloidal metal compoundpreferably has a positive charge. The colloidal metal compound having apositive charge is more effective in reducing the occurrence of knicksthan the colloidal metal compound having a negative charge. Inparticular, the colloidal metal compound having a positive charge ispreferably colloidal alumina.

The invention is particularly favorable when the polyvinyl alcohol-basedresin used in the adhesive for polarizing plate is a polyvinylalcohol-based resin having an acetoacetyl group. The adhesive using thepolyvinyl alcohol-based resin having an acetoacetyl group can form anadhesive layer with good water resistance. On the other hand, when apolyvinyl alcohol-based resin having an acetoacetyl group is used inconventional adhesive for polarizing plate, the occurrence of knicks isfrequently observed. However, the adhesive for polarizing plate of theinvention includes the colloidal metal compound and thus can reduce theoccurrence of knicks even when a polyvinyl alcohol-based resin having anacetoacetyl group is used in the adhesive for polarizing plate. Thus,there is provided an adhesive for polarizing plate having waterresistance and capable of reducing the occurrence of knicks.

In the adhesive for polarizing plate according, the crosslinking agentpreferably contains a methylol group-containing compound.

An amount of the crosslinking agent used in the adhesive for polarizingplate is preferably of 4 to 60 parts by weight based on 100 parts byweight of the polyvinyl alcohol-based resin.

The invention also relates to a polarizing plate, comprising: apolarizer; and a transparent protective film provided on at least oneside of the polarizer with an adhesive layer interposed therebetween,wherein the adhesive layer is formed of the adhesive for polarizingplate. In the polarizing plate according to the invention, the adhesivelayer contains the colloidal metal compound, so that the lamination ofthe polarizer and the transparent protective film is prevented fromforming knicks.

In the polarizing plate, the adhesive layer preferably has a thicknessof 10 nm to 300 nm, and the thickness of the adhesive layer ispreferably larger than the average particle size of the colloidal metalcompound contained in the adhesive for polarizing plate. If thethickness of the adhesive layer is set in the above range, the colloidalmetal compound can be almost uniformly dispersed in the adhesive layer.If the thickness of the adhesive layer is set larger than the averageparticle size of the colloidal metal compound, irregularities in thethickness of the adhesive layer can be reduced so that the formedadhesive layer can have good adhesion properties.

The invention also relates to a method for manufacturing a polarizingplate comprising a polarizer and a transparent protective film providedon at least one side of the polarizer with an adhesive layer interposedtherebetween, comprising the steps of: preparing the above-describedadhesive for polarizing plate; applying the adhesive for polarizingplate to an adhesive layer-receiving surface of the polarizer and/or anadhesive layer-receiving surface of the transparent protective film; andlaminating the polarizer and the transparent protective film.

The invention also relates to an optical film, comprising a laminateincluding at least one piece of the above-described polarizing plate.

The invention also relates to an image display, comprising theabove-described polarizing plate or optical film.

BEST MODE FOR CARRYING OUT THE INVENTION

The adhesive for polarizing plate of the invention is a resin solutionincluding a polyvinyl alcohol-based resin, a crosslinking agent and acolloidal metal compound with an average particle size of 1 to 100 nm.

The polyvinyl alcohol-based resin may be a polyvinyl alcohol resin or anpolyvinyl alcohol-based resin having an acetoacetyl group. The polyvinylalcohol-based resin having an acetoacetyl group can form a highlyreactive functional group-containing polyvinyl alcohol-based adhesiveand thus is preferred because it can increase the durability of thepolarizing plate.

Examples of polyvinyl alcohol-based resin include: a polyvinyl alcoholobtained by saponifying a polyvinyl acetate; a derivative thereof; asaponified copolymer of vinyl acetate and a monomer copolymerizabletherewith; and polyvinyl alcohols modified by acetalization,urethanization, etherification, grafting, phosphate esterification andthe like. Examples of the monomers include, unsaturated carboxylic acidssuch as maleic anhydride, fumaric acid, crotonic acid, itaconic acid and(meth) acrylic acid, and esters thereof; α-olefins such as ethylene andpropylene; (meth)allylsulfonic acid or sodium salt thereof,(meth)allylsulfonate; sodium sulfonate (monoalkyl maleate), sodiumdisulfonate (alkyl maleate); N-methylolacrylamide; an alkai salt ofacrylamide alkylsulfonate; N-vinylpyrrolidone, a derivative ofN-vinylpyrrolidone and the like. The polyvinyl alcohol-based resins canbe either used alone or in combination of two kinds or more.

While no specific limitation is imposed on a polyvinyl alcohol-basedresin, an average degree of polymerization is from about 100 to about5000, preferably from 1000 to 4000 and an average degree ofsaponification is from about 85 to about 100 mol %, preferably from 90to 100 mol % in consideration of adherence.

A polyvinyl alcohol-based resin having an acetoacetyl group is obtainedby reacting a polyvinyl alcohol-based resin and diketene to each otherwith a known method. Examples of known methods include: a method inwhich a polyvinyl alcohol-based resin is dispersed into a solvent suchas acetic acid, to which diketene is added and a method in which apolyvinyl alcohol-based resin is previously dissolved into a solventsuch as dimethylformamide or dioxane, to which diketene is added.Another example is a method in which diketene gas or diketene liquid isbrought into direct contact with a polyvinyl alcohol.

No specific limitation is imposed on a degree of modification by anacetoacetyl group in a polyvinyl alcohol-based resin having anacetoacetyl group or groups as far as the degree of modification is 0.1mol % or more. If the degree of modification is less than 0.1 mol %,water resistance of an adhesive layer is insufficient, which isimproper. A degree of modification by an acetoacetyl group is preferablyfrom about 0.1 to about 40 mol %, more preferably from 2 to 7 mol %. Ifa degree of modification by an acetoacetyl group exceeds 40 mol %,reaction sites with a crosslinking agent is fewer to thereby reduce aneffect of improvement on moisture resistance and heat resistance. Thedegree of modification by an acetoacetyl group is a value determined byNMR.

Any of crosslinking agents that have been used in a polyvinylalcohol-based adhesive can be used as a crosslinking agent in theinvention without a specific limitation thereon. A crosslinking agentthat can be used is a compound having at least two functional groupshaving reactivity with a polyvinyl alcohol-based resin. Examples thereofinclude: alkylene diamines having an alkylene group and two amino groupssuch as ethylene diamine, triethylene diamine and hexamethylene diamine;isocyanates such as tolylene diisocyanate, hydrogenated tolylenediisocyanate, trimethylolpropane tolylene diisocyanate adduct,triphenylmethane triisocyanate, methylenebis(4-phenylmethane)triisocyanate and isophorone diisocyanate, and ketoxime-blocked productsthereof or isocyanates of phenol-blocked products; epoxy compounds suchas ethylene glycol diglycidyl ether, polyethylene glycol diglycidylether, glycerin di- or triglicydyl ether, 1,6-hexanediol diglycidylether, trimethylolpropane triglycidyl ether, diglicidyl aniline anddiglycidyl amine; monoaldehydes such as formaldehyde, acetaldehyde,propionaldehyde and butylaldehyde; dialdehydes such as glyoxal,malonaldehyde, succindialdehyde, glutardialdehyde, maleic dialdehyde andphthaldialdehyde; amino-formaldehyde resins such as condensates withformaldehyde of methylolurea, methylolmelamine, alkylated methylolurea,alkylated methylolmelamine, acetoguanamine and benzoguanamine; salts ofdivalent metals or trivalent metals such as sodium, potassium,magnesium, calcium, aluminum, iron and nickel, and oxides of the metals.In particular, amino-formaldehyde resins and dialdehydes are preferred.Amino-formaldehyde resins preferably include methylol group-containingcompounds, and dialdehydes preferably include glyoxal. Methylolmelamine,a methylol group-containing compound, is particularly preferred. Thecrosslinking agent to be used may be a coupling agent such as a silanecoupling agent and a titanium coupling agent.

While the amount of the crosslinking agent to be blended may beappropriately determined depending on the type of the polyvinylalcohol-based resin and the like, it is generally from about 4 to about60 parts by weight, preferably from about 10 to about 55 parts byweight, more preferably from 20 to 50 parts by weight, based on 100parts by weight of the polyvinyl alcohol-based resin. In such ranges,good adhesion properties can be obtained.

In order to increase durability, a polyvinyl alcohol-based resin havingan acetoacetyl group is used. Also in this case, the crosslinking agentmay be used in an amount of about 4 to about 60 parts by weight,preferably in an amount of about 10 to about 55 parts by weight, morepreferably in an amount of 20 to 50 parts by weight, similarly to theabove, based on 100 parts by weight of the polyvinyl alcohol-basedresin. If the amount of the crosslinking agent to be blended is toolarge, the reaction of the crosslinking agent can proceed within a shorttime so that the adhesive can tend to form a gel, and as a result, theadhesive can have an extremely short pot life and thus can be difficultto use industrially. From these points of view, the crosslinking agentis used in the above amount, but the resin solution according to theinvention can be stably used even when the amount of the crosslinkingagent is large as mentioned above, because the resin solution containsthe colloidal metal compound.

The colloidal metal compound is a dispersion of fine particles in adispersion medium and can have permanent stability, because the fineparticles are electrostatically stabilized by the repulsion between thefine particles charged with the same type of charge. The colloidal metalcompound (fine particles) has an average particle size of 1 to 100 nm.If the average particle size of the colloid is in this range, the metalcompound can be almost uniformly dispersed in the adhesive layer so thatknicks can be prevented, while adhesive properties can be ensured. Theaverage particle size in this range is considerably smaller than thewavelength in the visible light range. Thus, the metal compound has noharmful effect on the polarization properties, even when the transmittedlight is scattered by the metal compound in the formed adhesive layer.The average particle size of the colloidal metal compound is preferablyfrom 1 to 100 nm, more preferably from 1 to 50 nm.

The colloidal metal compound to be used may be of various types.Examples of the colloidal metal compound include colloidal metal oxidessuch as colloidal alumina, colloidal silica, colloidal zirconia,colloidal titania, colloidal tin oxide, colloidal aluminum silicate,colloidal calcium carbonate, and colloidal magnesium silicate; colloidalmetal salts such as colloidal zinc carbonate, colloidal barium carbonateand colloidal calcium phosphate; and colloidal minerals such ascolloidal celite, colloidal talc, colloidal clay, and colloidal kaolin.

The colloidal metal compound may exist in the form of a colloidalsolution, in which the colloidal metal compound is dispersed in adispersion medium. The dispersion medium is generally water. Besideswater, any other dispersion medium such as alcohols may also be used.The concentration of the colloidal metal compound solid in the colloidalsolution is generally, but not limited to, from about 1 to about 50% byweight, more generally from 1 to 30% by weight. The colloidal metalcompound to be used may contain a stabilizing agent of an acid such asnitric acid, hydrochloric acid and acetic acid.

The colloidal metal compound is electrostatically stabilized and may beclassified into a positively charged one and a negatively charged one,while the colloidal metal compound is a non-electrically-conductivematerial. The positive charge and the negative charge are distinguisheddepending on the state of the colloidal surface charge in the solutionafter the preparation of the adhesive. For example, the charge of thecolloidal metal compound may be determined by measuring the zetapotential with a zeta potential meter. The surface charge of thecolloidal metal compound generally varies with pH. Thus, the charge ofthe colloidal solution state according to the invention is influenced bythe controlled pH of the adhesive solution. The pH of the adhesivesolution is generally set in the range of 2 to 6, preferably in therange of 2.5 to 5, more preferably in the range of 3 to 5, still morepreferably in the range of 3.5 to 4.5. In the invention, the colloidalmetal compound having a positive charge is more effective in reducingthe occurrence of knicks than the colloidal metal compound having anegative charge. Examples of the colloidal metal compound having apositive charge include colloidal alumina, colloidal zirconia, colloidaltitania, and colloidal tin oxide. In particular, colloidal alumina ispreferred.

The colloidal metal compound is added in an amount of 200 parts byweight or less (in solid weight) to 100 parts by weight of the polyvinylalcohol-based resin. If the amount ratio of the colloidal metal compoundis in the above range, the occurrence of knicks can be reduced, whilethe adhesion between the polarizer and the transparent protective filmcan be ensured. The amount ratio of the colloidal metal compound ispreferably from 10 to 200 parts by weight, more preferably from 20 to175 parts by weight, still more preferably from 30 to 150 parts byweight. If the amount ratio of the colloidal metal compound is more than200 parts by weight based on 100 parts by weight of the polyvinylalcohol-based resin, the content of the polyvinyl alcohol-based resin inthe adhesive can be reduced to a low level, which is undesirable in viewof adhesion properties. While there is no particular limitation to thelower limit to the amount ratio of the colloidal metal compound, thelower limit is preferably in the above range for effective prevention ofknicks.

The adhesive for polarizing plate of the invention is a resin solutionincluding the polyvinyl alcohol-based resin, the crosslinking agent andthe colloidal metal compound with an average particle size of 1 to 100nm and generally used in the form of an aqueous solution. While theresin solution may have any concentration, it preferably has aconcentration of 0.1 to 15% by weight, more preferably of 0.5 to 10% byweight, in view of coatability, shelf stability and the like.

The viscosity of the resin solution, which is used as the adhesive forpolarizing plate, is generally, but not limited to, from 1 to 50 mPa·s.In the preparation of conventional polarizing plates, the occurrence ofknicks tends to increase as the viscosity of a resin solution decreases.Using the adhesive for polarizing plate of the invention, however, theoccurrence of knicks can be prevented even in a low viscosity range suchas the range of 1 to 20 mPa·s, and thus the occurrence of knicks can beprevented regardless of the viscosity of the resin solution. Polyvinylalcohol-based resin having an acetoacetyl groups cannot have high degreeof polymerization in contrast to other general polyvinyl alcohol resins,and therefore they are used at a low viscosity as mentioned above.According to the invention, however, knicks, which would otherwise becaused by the low viscosity of the resin solution, can be prevented fromoccurring even when the polyvinyl alcohol-based resin having anacetoacetyl group is being used.

The resin solution for use as the adhesive for polarizing plate may beprepared by any method. In general, the resin solution may be preparedby a process that includes mixing the polyvinyl alcohol-based resin andthe crosslinking agent, appropriately adjusting the concentrationthereof, and then adding the colloidal metal compound to the mixture.Optionally, a polyvinyl alcohol-based resin having an acetoacetyl groupmay be used as the polyvinyl alcohol-based resin. When the crosslinkingagent is added in a relatively large amount, the stability of thesolution may be taken into account, and therefore the mixing of thepolyvinyl alcohol-based resin and the colloidal metal compound may befollowed by the addition of the crosslinking agent in consideration ofthe timing of using the resulting resin solution and so on. Theconcentration of the resin solution for use as the adhesive forpolarizing plate may be adjusted as appropriate, after the resinsolution is prepared.

The adhesive for polarizing plate may also contain various types oftackifiers, stabilizing agents such as ultraviolet absorbing agents,antioxidants, heat-resistant stabilizing agents, andhydrolysis-resistant stabilizing agents, and so on. In the invention,the colloidal metal compound, which is a non-electrically-conductivematerial, may also contain fine particles of an electrically-conductivematerial.

A polarizing plate of the invention is manufactured by adhere atransparent protective film to a polarizer with the adhesive. In theobtained polarizing plate, a transparent protective film or transparentprotective films are provided on one surface or both surfaces of apolarizer with an adhesive agent layer formed with the adhesive forpolarizing plate interposed therebetween.

Coating of the adhesive may be performed on one/or both of thetransparent protective film and the polarizer. Coating of the adhesiveis preferably conducted so as to achieve a thickness after drying of theorder in the range of from 10 to 300 nm. The thickness of the adhesivelayer is more preferably from 10 to 200 nm, still more preferably from20 to 150 nm, in terms of achieving uniform in-plane thickness andsufficient adhesive force. At described above, the thickness of theadhesive layer is preferably designed to be larger than the averageparticle size of the colloidal metal compound contained in the adhesivefor polarizing plate.

Examples of methods for controlling the thickness of the adhesive layerinclude, but are not limited to, methods including controlling the solidconcentration of the adhesive solution or controlling an adhesivecoater. While the thickness of the adhesive layer may be measured by anymethod, cross-sectional observation measurement by SEM (ScanningElectron Microscopy) or TEM (Transmission Electron Microscopy) ispreferably used. The adhesive may be applied by any process, and variousmethods such as roll methods, spraying methods, and immersion methodsmay be used for the application.

After the adhesive is coated, the transparent protective is adhered tothe polarizer with a roll laminator or the like. After adhesion, adrying step is performed to thereby form an adhesive layer that is a drycoated layer. A drying temperature is from about 5 to about 150° C.preferably from 30 to 120° C. and for a time of 120 sec or longer,preferably for a time 300 sec or longer.

A polarizer is not limited especially but various kinds of polarizer maybe used. As a polarizer, for example, a film that is uniaxiallystretched after having dichromatic substances, such as iodine anddichromatic dye, absorbed to hydrophilic high molecular weight polymerfilms, such as polyvinyl alcohol type film, partially formalizedpolyvinyl alcohol type film, and ethylene-vinyl acetate copolymer typepartially saponified film; poly-ene type orientation films, such asdehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride,etc. may be mentioned. In these, a polyvinyl alcohol type film comprisesdichromatic materials such as iodine, dichromatic dye is suitably used.Although thickness of polarizer is not especially limited, the thicknessof about 5 to about 80 μm is commonly adopted.

A polarizer that is uniaxially stretched after a polyvinyl alcohol typefilm dyed with iodine is obtained by stretching a polyvinyl alcohol filmby 3 to 7 times the original length, after dipped and dyed in aqueoussolution of iodine. If needed the film may also be dipped in aqueoussolutions, such as boric acid and potassium iodide. Furthermore, beforedyeing, the polyvinyl alcohol type film may be dipped in water andrinsed if needed. By rinsing polyvinyl alcohol type film with water,effect of preventing un-uniformity, such as unevenness of dyeing, isexpected by making polyvinyl alcohol type film swelled in addition thatalso soils and blocking inhibitors on the polyvinyl alcohol type filmsurface may be washed off. Stretching may be applied after dyed withiodine or may be applied concurrently, or conversely dyeing with iodinemay be applied after stretching. Stretching is applicable in aqueoussolutions, such as boric acid and potassium iodide, and in water bath.

Preferable Materials that form the transparent protective film, which isprovided one side or both sides of the polarizer is the material havingoutstanding transparency, mechanical strength, heat stability andoutstanding moisture interception property, or the like. As materials ofthe above-mentioned transparent protective film, for example, polyestertype polymers, such as polyethylene terephthalate andpolyethylenenaphthalate; cellulose type polymers, such as diacetylcellulose and triacetyl cellulose; acrylics type polymer, such as polymethylmethacrylate; styrene type polymers, such as polystyrene andacrylonitrile-styrene copolymer (AS resin); polycarbonate type polymermay be mentioned. Besides, as examples of the polymer forming atransparent protective film, polyolefin type polymers, such aspolyethylene, polypropylene, polyolefin that has cyclo-type ornorbornene structure, ethylene-propylene copolymer; vinyl chloride typepolymer; amide type polymers, such as nylon and aromatic polyamide;imide type polymers; sulfone type polymers; polyether sulfone typepolymers; polyether-ether ketone type polymers; poly phenylene sulfidetype polymers; vinyl alcohol type polymer; vinylidene chloride typepolymers; vinyl butyral type polymers; arylate type polymers;polyoxymethylene type polymers; epoxy type polymers; or blend polymersof the above-mentioned polymers may be mentioned. The transparentprotective film is generally laminated to the polarizer with theadhesive layer, but thermosetting resins or ultraviolet curing resinssuch as (meth)acrylic, urethane, acrylic urethane, epoxy, or siliconeresins may be used for the transparent protective film. The transparentprotective film may also contain at least one type of any appropriateadditive. Examples of the additive include an ultraviolet absorbingagent, an antioxidant, a lubricant, a plasticizer, a release agent, ananti-discoloration agent, a flame retardant, a nucleating agent, anantistatic agent, a pigment, and a colorant. The content of thethermoplastic resin in the transparent protective film is preferablyfrom 50 to 100% by weight, more preferably from 50 to 99% by weight,still more preferably from 60 to 98% by weight, particularly preferablyfrom 70 to 97% by weight. If the content of the thermoplastic resin inthe transparent protective film is 50% by weight or less, hightransparency and other properties inherent in the thermoplastic resincan fail to be sufficiently exhibited.

Moreover, as is described in JP-A No. 2001-343529 (WO 01/37007), polymerfilms, for example, resin compositions including (A) thermoplasticresins having substituted and/or non-substituted imido group insidechain, and (B) thermoplastic resins having substituted and/ornon-substituted phenyl and nitrile group in sidechain may be mentioned.As an illustrative example, a film may be mentioned that is made of aresin composition including alternating copolymer comprisingiso-butylene and N-methyl maleimide, and acrylonitrile-styrenecopolymer. A film comprising mixture extruded article of resincompositions etc. may be used. Since the films are less in retardationand less in photoelastic coefficient, faults such as unevenness due to astrain in a polarizing plate can be removed and besides, since they areless in moisture permeability, they are excellent in durability underhumidified environment.

Thickness of the transparent protective film can be properly determinedand generally in the range of from about 1 to about 500 μm from theviewpoint of a strength, workability such as handlability, requirementfor a thin film and the like. Especially, the thickness is preferably inthe range of from 1 to 300 μm and more preferably in the range of from 5to 200 μm. Knicks tend to occur as the thickness of the transparentprotective film decreases. Therefore, it is particularly preferred thatthe transparent protective film has a thickness of 5 to 100 μm.

Note that in a case where the transparent protective films are providedon both sides of a polarizer, the protective films made from the samepolymer may be used on both sides thereof or alternatively, theprotective films made from polymer materials different from each othermay also be used on respective both sides thereof.

At least one selected from a cellulose resin, a polycarbonate resin, acyclic polyolefin resin, and a (meth)acrylic resin is preferably usedfor the transparent protective film according to the invention.

The cellulose resin is an ester of cellulose and a fatty acid. Examplesof such a cellulose ester resin include triacetyl cellulose, diacetylcellulose, tripropionyl cellulose, dipropionyl cellulose, and the like.In particular, triacetyl cellulose is preferred. Much commerciallyavailable triacetyl celluloses are placing on sale and are advantageousin view of easy availability and cost. Examples of commerciallyavailable products of triacetyl cellulose include UV-50, UV-80, SH-80,TD-80U, TD-TAC, and UZ-TAC (trade names) manufactured by FujifilmCorporation, and KC series manufactured by Konica Minolta. In general,these triacetyl cellulose products have a thickness directionretardation (Rth) of about 60 nm or less, while having an in-planeretardation (Re) of almost zero.

Cellulose resin films with relatively small thickness directionretardation may be obtained by processing any of the above celluloseresins. Examples of the processing method include a method that includeslaminating a general cellulose-based film to a base film such as apolyethylene terephthalate, polypropylene, or stainless steel film,coated with a solvent such as cyclopentanone or methyl ethyl ketone,drying the laminate by heating (for example, at 80 to 150° C. for 3 to10 minutes) and then separating the base film; and a method thatincludes coating a general cellulose resin film with a solution of anorbornene resin, a (meth)acrylic resin or the like in a solvent such ascyclopentanone or methyl ethyl ketone, drying the coated film by heating(for example, at 80 to 150° C. for 3 to 10 minutes), and then separatingthe coating.

The cellulose resin film with a relatively small thickness directionretardation to be used may be a fatty acid cellulose resin film with acontrolled degree of fat substitution. While triacetyl cellulose forgeneral use has a degree of acetic acid substitution of about 2.8,preferably, the degree of acetic acid substitution is controlled to 1.8to 2.7, more preferably, the degree of propionic acid substitution iscontrolled to 0.1 to 1, so that the Rth can be reduced. The Rth may alsobe controlled to be low by adding a plasticizer such as dibutylphthalate, p-toluenesulfonanilide, and acetyl triethyl citrate, to thefatty acid-substituted cellulose resin. The plasticizer is preferablyadded in amount of 40 parts by weight or less, more preferably of 1 to20 parts by weight, still more preferably of 1 to 15 parts by weight, to100 parts by weight of the fatty acid cellulose resin.

For example, the cyclic polyolefin resin is preferably a norborneneresin. Cyclic olefin resin is a generic name for resins produced bypolymerization of cyclic olefin used as a polymerizable unit, andexamples thereof include the resins disclosed in JP-A Nos. 01-240517,03-14882, and 03-122137. Specific examples thereof include ring-opened(co)polymers of cyclic olefins, addition polymers of cyclic olefins,copolymers (typically random copolymers) of cyclic olefins and α-olefinssuch as ethylene and propylene, graft polymers produced by modificationthereof with unsaturated carboxylic acids or derivatives thereof, andhydrides thereof. Examples of the cyclic olefin include norbornenemonomers.

Various commercially available cyclic polyolefin resins are placing onsale. Examples thereof include Zeonex (trade name) and Zeonor (tradename) series manufactured by Zeon Corporation, Arton (trade name) seriesmanufactured by JSR Corporation, Topas (trade name) series manufacturedby Ticona, and Apel (trade name) series manufactured by MitsuiChemicals, Inc.

The (meth)acrylic resin preferably has a glass transition temperature(Tg) of 115° C. or more, more preferably of 120° C. or more, still morepreferably of 125° C. or more, particularly preferably of 130° C. ormore. If the Tg is 115° C. or more, the resulting polarizing plate canhave good durability. The upper limit to the Tg of the (meth)acrylicresin is preferably, but not limited to, 170° C. or less, in view offormability and the like. The (meth)acrylic resin can form a film withan in-plane retardation (Re) of almost zero and a thickness directionretardation (Rth) of almost zero.

Any appropriate (meth)acrylic resin may be used as long as theadvantages of the invention are not reduced. Examples of such a(meth)acrylic resin include poly(meth)acrylate such as poly(methylmethacrylate), methyl methacrylate-(meth)acrylic acid copolymers, methylmethacrylate-(meth)acrylate copolymers, methylmethacrylate-acrylate-(meth)acrylic acid copolymers, methyl(meth)acrylate-styrene copolymers (such as MS resins), and alicyclichydrocarbon group-containing polymers (such as methylmethacrylate-cyclohexyl methacrylate copolymers and methylmethacrylate-norbornyl(meth)acrylate copolymers). Poly(C₁₋₆ alkyl(meth)acrylate) such as poly(methyl(meth)acrylate) is preferred, and amethyl methacrylate-based resin mainly composed of a methyl methacrylateunit (50 to 100% by weight, preferably 70 to 100% by weight) is morepreferred.

Examples of the (meth)acrylic resin include Acrypet VH and AcrypetVRL20A each manufactured by Mitsubishi Rayon Co., Ltd., (meth)acrylicresins having a ring structure in their molecule as disclosed in JP-ANo. 2004-70296, and high-Tg (meth)acrylic resins produced byintramolecular crosslinking or intramolecular cyclization reaction.

Lactone ring structure-containing (meth)acrylic resins may also be used,because they have high heat resistance and high transparency and alsohave high mechanical strength after biaxially stretched.

Examples of the lactone ring structure-containing (meth)acrylic reinsinclude the lactone ring structure-containing (meth)acrylic reinsdisclosed in JP-A Nos. 2000-230016, 2001-151814, 2002-120326,2002-254544, and 2005-146084.

The lactone ring structure-containing (meth)acrylic reins preferablyhave a ring structure represented by Formula (I):

wherein R¹, R² and R³ each independently represent a hydrogen atom or anorganic residue of 1 to 20 carbon atoms. The organic residue may containan oxygen atom(s).

The content of the lactone ring structure represented by Formula (I) inthe lactone ring structure-containing (meth)acrylic resin is preferablyfrom 5 to 90% by weight, more preferably from 10 to 70% by weight, stillmore preferably from 10 to 60% by weight, particularly preferably from10 to 50% by weight. If the content of the lactone ring structurerepresented by Formula (I) in the lactone ring structure-containing(meth)acrylic resin is less than 5% by weight, its heat resistance,solvent resistance or surface hardness can be insufficient. If thecontent of the lactone ring structure represented by Formula (I) in thelactone ring structure-containing (meth)acrylic resin is more than 90%by weight, its formability or workability can be poor.

The lactone ring structure-containing (meth)acrylic resin preferably hasa mass average molecular weight (also referred to as weight averagemolecular weight) of 1,000 to 2,000,000, more preferably of 5,000 to1,000,000, still more preferably of 10,000 to 500,000, particularlypreferably of 50,000 to 500,000. A mass average molecular weight outsidethe above range is not preferred in view of formability or workability.

The lactone ring structure-containing (meth)acrylic resin preferably hasa Tg of 115° C. or more, more preferably of 120° C. or more, still morepreferably of 125° C. or more, particularly preferably of 130° C. ormore. For example, the resin with a Tg of 115° C. or more can producegood durability, when it is incorporated in the form of a transparentprotective film in a polarizing plate. The upper limit to the Tg of thelactone ring structure-containing (meth)acrylic resin is preferably, butnot limited to, 170° C. or less in view of formability and the like.

The total light transmittance of the lactone ring structure-containing(meth)acrylic resin, which may be measured according to ASTM-D-1003 withrespect to injection molded products, is preferably as high as possible,and specifically, it is preferably 85% or more, more preferably 88% ormore, still more preferably 90% or more. The total light transmittanceis an index of transparency, and a total light transmittance of lessthan 85% can result in reduced transparency.

The transparent protective film to be used generally has an in-planeretardation of less than 40 nm and a thickness direction retardation ofless than 80 nm. The in-plane retardation Re is expressed by the formulaRe=(nx−ny)×d, the thickness direction retardation Rth is expressed bythe formula Rth=(nx−nz)×d, and the Nz coefficient is represented by theformula Nz=(nx−nz)/(nx−ny), where nx, ny and nz are the refractiveindices of the film in the directions of its slow axis, fast axis andthickness, respectively, d is the thickness (nm) of the film, and thedirection of the slow axis is a direction in which the in-planerefractive index of the film is maximum. Moreover, it is preferable thatthe transparent protective film may have as little coloring as possible.A protective film having a thickness direction retardation of from −90nm to +75 nm may be preferably used. Thus, coloring (optical coloring)of polarizing plate resulting from a protective film may mostly becancelled using a protective film having a thickness directionretardation (Rth) of from −90 nm to +75 nm. The thickness directionretardation (Rth) is preferably from −80 nm to +60 nm, and especiallypreferably from −70 nm to +45 nm.

Alternatively, the transparent protective film to be used may be aretardation plate having an in-plane retardation of 40 nm or more and/ora thickness direction retardation of 80 nm or more. The in-planeretardation is generally controlled in the range of 40 to 200 nm, andthe thickness direction retardation is generally controlled in the rangeof 80 to 300 nm. The retardation plate for use as the transparentprotective film also has the function of the transparent protective filmand thus can contribute to a reduction in thickness.

Examples of the retardation plate include a birefringent film producedby uniaxially or biaxially stretching a polymer material, an orientedliquid crystal polymer film, and an oriented liquid crystal polymerlayer supported on a film. The thickness of the retardation plate isgenerally, but not limited to, from about 20 to about 150 μm.

Examples of the polymer material include polyvinyl alcohol, polyvinylbutyral, poly(methyl vinyl ether), poly(hydroxyethyl acrylate),hydroxyethyl cellulose, hydroxypropyl cellulose, methylcellulose,polycarbonate, polyarylate, polysulfone, polyethylene terephthalate,polyethylene naphthalate, polyethersulfone, polyphenylene sulfide,polyphenylene oxide, polyallylsulfone, polyamide, polyimide, polyolefin,polyvinyl chloride, cellulose resins, cyclic polyolefin resins(norbornene reins), and various types of binary or ternary copolymersthereof, graft copolymers thereof, and any blend thereof. Any of thesepolymer materials may be formed into an oriented product (a stretchedfilm) by stretching or the like.

Examples of the liquid crystal polymer include various main-chain orside-chain types having a liquid crystal molecular orientationproperty-imparting conjugated linear atomic group (mesogen) introducedin a main or side chain of a polymer. Examples of the main chain typeliquid crystal polymer include polymers having a mesogen group bondedthereto via a flexibility-imparting spacer moiety, such as nomadicallyordered polyester liquid-crystalline polymers, discotic polymers, andcholesteric polymers. For example, the side-chain type liquid crystalpolymer may be a polymer comprising: a main chain skeleton ofpolysiloxane, polyacrylate, polymethacrylate, or polymalonate; and aside chain having a mesogen moiety that comprises a nematicorientation-imparting para-substituted cyclic compound unit and isbonded thereto via a spacer moiety comprising a conjugated atomic group.For example, any of these liquid crystal polymers may be applied by aprocess that includes spreading a solution of the liquid crystallinepolymer on an alignment surface such as a rubbed surface of a thin filmof polyimide, polyvinyl alcohol or the like, formed on the glass plate,and an obliquely vapor-deposited silicon oxide surface, andheat-treating it.

The retardation plate may have any appropriate retardation depending onthe intended use such as compensation for coloration, viewing angle, orthe like due to the birefringence of various wave plates or liquidcrystal layers. Two or more types of retardation plates may also belaminated to provide controlled optical properties, includingretardation.

A retardation plate satisfying the relation: nx=ny>nz, nx>ny>nz,nx>ny=nz, nx>nz>ny, nz=nx>ny, nz>nx>ny, or nz>nx=ny may be selected andused depending on various applications. The relation ny=nz includes notonly the case where ny is completely equal to nz but also the case whereny is substantially equal to nz.

For example, the retardation plate satisfying the relation nx>ny>nz tobe used preferably has a in-plane retardation of 40 to 100 nm, athickness retardation of 100 to 320 nm, and an Nz coefficient of 1.8 to4.5. For example, the retardation plate satisfying the relation nx>ny=nz(positive A plate) to be used preferably has a in-plane retardation of100 to 200 nm. For example, the retardation plate satisfying therelation nz=nx>ny (negative A plate) to be used preferably has ain-plane retardation of 100 to 200 nm. For example, the retardationplate satisfying the relation nx>nz>ny to be used preferably has ain-plane retardation of 150 to 300 nm and an Nz coefficient of more than0 and not more than 0.7. As described above, for example, theretardation plate satisfying the relation nx=ny>nz, nz>nx>ny or nz>nx=nymay also be used.

The transparent protective film may be appropriately selected dependingon the liquid crystal display to be produced therewith. In the case ofVA (Vertical Alignment, including MVA and PVA), it is preferred that thetransparent protective film on at least one side of the polarizing plate(on the cell side) has a retardation. Specifically, it preferably has aretardation Re in the range of 0 to 240 nm and a retardation Rth in therange of 0 to 500 nm. In terms of three-dimensional refractive index,the case of nx>ny=nz, nx>ny>nz, nx>nz>ny, or nx=ny>nz (uniaxial,biaxial, Z conversion, negative C-plate) is preferred. When polarizingplates are used on upper and lower sides of a liquid crystal cell, thetransparent protective films may have a retardation on upper and lowersides of the liquid crystal cell, or one of the upper and lowertransparent protective films may has a retardation.

For example, in the case of IPS (In-Plane Switching, including FFS), thetransparent protective film for use in one of the polarizing plates mayhave or may not have a retardation. For example, a transparentprotective film with no retardation is preferably provided on both upperand lower sides of a liquid crystal cell (cell sides), or otherwise atransparent protective film with a retardation is preferably provided onboth or one of the upper and lower sides of a liquid crystal cell (forexample, Z conversion on the upper side with no retardation on the lowerside or an A-plate provided on the upper side with a positive C-plateprovided on the lower side). When it has a retardation, it preferablyhas a retardation Re in the range of −500 to 500 nm and a retardationRth in the range of −500 to 500 nm. In terms of three-dimensionalrefractive index, nx>ny=nz, nx>nz>ny, nz>nx=ny, or nz>nx>ny (uniaxial, Zconversion, positive C-plate, positive A-plate) is preferred.

The film with a retardation may be separately prepared and laminated toa transparent protective film with no retardation so that the functiondescribed above can be provided.

An easy adhesion treatment can be applied onto a surface of atransparent protective film which is adhered to a polarizer. Examples ofeasy adhesion treatments include: dry treatments such as a plasmatreatment and a corona treatment; chemical treatment such as alkalinetreatment (saponification); and a coating treatment in which an easyadhesion layer is formed. Among them, preferable are a coating treatmentand an alkaline treatment each forming an easy adhesion layer. Information of an easy adhesion layer, there can be used each of variouskinds of easy adhesion materials such as a polyol resin, apolycarboxylic resin and a polyester resin. Note that a thickness of aneasy adhesion layer is preferably usually from about 0.001 to about 10μm, more preferably from about 0.001 to about 5 μm and especiallypreferably from about 0.001 to about 1 μm.

A hard coat layer may be prepared, or antireflection processing,processing aiming at sticking prevention, diffusion or anti glare may beperformed onto the face on which the polarizing film of the abovedescribed transparent protective film has not been adhered.

A hard coat processing is applied for the purpose of protecting thesurface of the polarizing plate from damage, and this hard coat film maybe formed by a method in which, for example, a curable coated film withexcellent hardness, slide property etc. is added on the surface of theprotective film using suitable ultraviolet curable type resins, such asacrylic type and silicone type resins. Antireflection processing isapplied for the purpose of antireflection of outdoor daylight on thesurface of a polarizing plate and it may be prepared by forming anantireflection film according to the conventional method etc. Besides, asticking prevention processing is applied for the purpose of adherenceprevention with adjoining layer.

In addition, an anti glare processing is applied in order to prevent adisadvantage that outdoor daylight reflects on the surface of apolarizing plate to disturb visual recognition of transmitting lightthrough the polarizing plate, and the processing may be applied, forexample, by giving a fine concavo-convex structure to a surface of theprotective film using, for example, a suitable method, such as roughsurfacing treatment method by sandblasting or embossing and a method ofcombining transparent fine particle. As a fine particle combined inorder to form a fine concavo-convex structure on the above-mentionedsurface, transparent fine particles whose average particle size is 0.5to 50 μm, for example, such as inorganic type fine particles that mayhave conductivity comprising silica, alumina, titania, zirconia, tinoxides, indium oxides, cadmium oxides, antimony oxides, etc., andorganic type fine particles comprising cross-linked of non-cross-linkedpolymers may be used. When forming fine concavo-convex structure on thesurface, the amount of fine particle used is usually about 2 to 70weight parts to the transparent resin 100 weight parts that forms thefine concavo-convex structure on the surface, and preferably 5 to 50weight parts. An anti glare layer may serve as a diffusion layer(viewing angle expanding function etc.) for diffusing transmitting lightthrough the polarizing plate and expanding a viewing angle etc.

In addition, the above-mentioned antireflection layer, stickingprevention layer, diffusion layer, anti glare layer, etc. may be builtin the protective film itself, and also they may be prepared as anoptical layer different from the protective film.

A polarizing plate of the present invention may be used in practical useas an optical film laminated with other optical layers. Although thereis especially no limitation about the optical layers, one layer or twolayers or more of optical layers, which may be used for formation of aliquid crystal display etc., such as a reflector, a transflective plate,a retardation plate (a half wavelength plate and a quarter wavelengthplate included), and a viewing angle compensation film, may be used.Especially preferable polarizing plates are; a reflection typepolarizing plate or a transflective type polarizing plate in which areflector or a transflective reflector is further laminated onto apolarizing plate of the present invention; an elliptically polarizingplate or a circular polarizing plate in which a retardation plate isfurther laminated onto the polarizing plate; a wide viewing anglepolarizing plate in which a viewing angle compensation film is furtherlaminated onto the polarizing plate; or a polarizing plate in which abrightness enhancement film is further laminated onto the polarizingplate.

A reflective layer is prepared on a polarizing plate to give areflection type polarizing plate, and this type of plate is used for aliquid crystal display in which an incident light from a view side(display side) is reflected to give a display. This type of plate doesnot require built-in light sources, such as a backlight, but has anadvantage that a liquid crystal display may easily be made thinner. Areflection type polarizing plate may be formed using suitable methods,such as a method in which a reflective layer of metal etc. is, ifrequired, attached to one side of a polarizing plate through atransparent protective film etc.

As an example of a reflection type polarizing plate, a plate may bementioned on which, if required, a reflective layer is formed using amethod of attaching a foil and vapor deposition film of reflectivemetals, such as aluminum, to one side of a matte treated protectivefilm. Moreover, a different type of plate with a fine concavo-convexstructure on the surface obtained by mixing fine particle into theabove-mentioned protective film, on which a reflective layer ofconcavo-convex structure is prepared, may be mentioned. The reflectivelayer that has the above-mentioned fine concavo-convex structurediffuses incident light by random reflection to prevent directivity andglaring appearance, and has an advantage of controlling unevenness oflight and darkness etc. Moreover, the protective film containing thefine particle has an advantage that unevenness of light and darkness maybe controlled more effectively, as a result that an incident light andits reflected light that is transmitted through the film are diffused. Areflective layer with fine concavo-convex structure on the surfaceeffected by a surface fine concavo-convex structure of a protective filmmay be formed by a method of attaching a metal to the surface of atransparent protective film directly using, for example, suitablemethods of a vacuum evaporation method, such as a vacuum depositionmethod, an ion plating method, and a sputtering method, and a platingmethod etc.

Instead of a method in which a reflection plate is directly given to theprotective film of the above-mentioned polarizing plate, a reflectionplate may also be used as a reflective sheet constituted by preparing areflective layer on the suitable film for the transparent film. Inaddition, since a reflective layer is usually made of metal, it isdesirable that the reflective side is covered with a protective film ora polarizing plate etc. when used, from a viewpoint of preventingdeterioration in reflectance by oxidation, of maintaining an initialreflectance for a long period of time and of avoiding preparation of aprotective layer separately etc.

In addition, a transflective type polarizing plate may be obtained bypreparing the above-mentioned reflective layer as a transflective typereflective layer, such as a half-mirror etc. that reflects and transmitslight. A transflective type polarizing plate is usually prepared in thebackside of a liquid crystal cell and it may form a liquid crystaldisplay unit of a type in which a picture is displayed by an incidentlight reflected from a view side (display side) when used in acomparatively well-lighted atmosphere. And this unit displays a picture,in a comparatively dark atmosphere, using embedded type light sources,such as a back light built in backside of a transflective typepolarizing plate. That is, the transflective type polarizing plate isuseful to obtain of a liquid crystal display of the type that savesenergy of light sources, such as a back light, in a well-lightedatmosphere, and can be used with a built-in light source if needed in acomparatively dark atmosphere etc.

A description of the elliptically polarizing plate or circularlypolarizing plate in which the retardation plate is laminated to thepolarizing plate will be made in the following paragraph. Thesepolarizing plates change linearly polarized light into ellipticallypolarized light or circularly polarized light, elliptically polarizedlight or circularly polarized light into linearly polarized light orchange the polarization direction of linearly polarization by a functionof the retardation plate. As a retardation plate that changes circularlypolarized light into linearly polarized light or linearly polarizedlight into circularly polarized light, what is called a quarterwavelength plate (also called λ/4 plate) is used. Usually,half-wavelength plate (also called λ/2 plate) is used, when changing thepolarization direction of linearly polarized light.

Elliptically polarizing plate is effectively used to give a monochromedisplay without above-mentioned coloring by compensating (preventing)coloring (blue or yellow color) produced by birefringence of a liquidcrystal layer of a super twisted nematic (STN) type liquid crystaldisplay. Furthermore, a polarizing plate in which three-dimensionalrefractive index is controlled may also preferably compensate (prevent)coloring produced when a screen of a liquid crystal display is viewedfrom an oblique direction. Circularly polarizing plate is effectivelyused, for example, when adjusting a color tone of a picture of areflection type liquid crystal display that provides a colored picture,and it also has function of antireflection. For example, a retardationplate may be used that compensates coloring and viewing angle, etc.caused by birefringence of various wavelength plates or liquid crystallayers etc. Besides, optical characteristics, such as retardation, maybe controlled using laminated layer with two or more sorts ofretardation plates having suitable retardation value according to eachpurpose. As retardation plates, birefringence films formed by stretchingfilms comprising suitable polymers, such as polycarbonates, norbornenetype resins, polyvinyl alcohols, polystyrenes, poly methylmethacrylates, polypropylene; polyarylates and polyamides; aligned filmscomprising liquid crystal materials, such as liquid crystal polymer; andfilms on which an alignment layer of a liquid crystal material issupported may be mentioned. A retardation plate may be a retardationplate that has a proper retardation according to the purposes of use,such as various kinds of wavelength plates and plates aiming atcompensation of coloring by birefringence of a liquid crystal layer andof visual angle, etc., and may be a retardation plate in which two ormore sorts of retardation plates is laminated so that opticalproperties, such as retardation, may be controlled.

The above-mentioned elliptically polarizing plate and an above-mentionedreflected type elliptically polarizing plate are laminated platecombining suitably a polarizing plate or a reflection type polarizingplate with a retardation plate. This type of elliptically polarizingplate etc. may be manufactured by combining a polarizing plate(reflected type) and a retardation plate, and by laminating them one byone separately in the manufacture process of a liquid crystal display.On the other hand, the polarizing plate in which lamination wasbeforehand carried out and was obtained as an optical film, such as anelliptically polarizing plate, is excellent in a stable quality, aworkability in lamination etc., and has an advantage in improvedmanufacturing efficiency of a liquid crystal display.

A viewing angle compensation film is a film for extending viewing angleso that a picture may look comparatively clearly, even when it is viewedfrom an oblique direction not from vertical direction to a screen. Assuch a viewing angle compensation retardation plate, in addition, a filmhaving birefringence property that is processed by uniaxial stretchingor orthogonal biaxial stretching and a biaxial stretched film asinclined alignment film etc. may be used. As inclined alignment film,for example, a film obtained using a method in which a heat shrinkingfilm is adhered to a polymer film, and then the combined film is heatedand stretched or shrunk under a condition of being influenced by ashrinking force, or a film that is aligned in oblique direction may bementioned. The viewing angle compensation film is suitably combined forthe purpose of prevention of coloring caused by change of visible anglebased on retardation by liquid crystal cell etc. and of expansion ofviewing angle with good visibility.

Besides, a compensation plate in which an optical anisotropy layerconsisting of an alignment layer of liquid crystal polymer, especiallyconsisting of an inclined alignment layer of discotic liquid crystalpolymer is supported with triacetyl cellulose film may preferably beused from a viewpoint of attaining a wide viewing angle with goodvisibility.

The polarizing plate with which a polarizing plate and a brightnessenhancement film are adhered together is usually used being prepared ina backside of a liquid crystal cell. A brightness enhancement film showsa characteristic that reflects linearly polarized light with apredetermined polarization axis, or circularly polarized light with apredetermined direction, and that transmits other light, when naturallight by back lights of a liquid crystal display or by reflection from aback-side etc., comes in. The polarizing plate, which is obtained bylaminating a brightness enhancement film to a polarizing plate, thusdoes not transmit light without the predetermined polarization state andreflects it, while obtaining transmitted light with the predeterminedpolarization state by accepting a light from light sources, such as abacklight. This polarizing plate makes the light reflected by thebrightness enhancement film further reversed through the reflectivelayer prepared in the backside and forces the light re-enter into thebrightness enhancement film, and increases the quantity of thetransmitted light through the brightness enhancement film bytransmitting a part or all of the light as light with the predeterminedpolarization state. The polarizing plate simultaneously suppliespolarized light that is difficult to be absorbed in a polarizer, andincreases the quantity of the light usable for a liquid crystal picturedisplay etc., and as a result luminosity may be improved. That is, inthe case where the light enters through a polarizer from backside of aliquid crystal cell by the back light etc. without using a brightnessenhancement film, most of the light, with a polarization directiondifferent from the polarization axis of a polarizer, is absorbed by thepolarizer, and does not transmit through the polarizer. This means thatalthough influenced with the characteristics of the polarizer used,about 50 percent of light is absorbed by the polarizer, the quantity ofthe light usable for a liquid crystal picture display etc. decreases somuch, and a resulting picture displayed becomes dark. A brightnessenhancement film does not enter the light with the polarizing directionabsorbed by the polarizer into the polarizer but reflects the light onceby the brightness enhancement film, and further makes the light reversedthrough the reflective layer etc. prepared in the backside to re-enterthe light into the brightness enhancement film. By this above-mentionedrepeated operation, only when the polarization direction of the lightreflected and reversed between the both becomes to have the polarizationdirection which may pass a polarizer, the brightness enhancement filmtransmits the light to supply it to the polarizer. As a result, thelight from a backlight may be efficiently used for the display of thepicture of a liquid crystal display to obtain a bright screen.

A diffusion plate may also be prepared between brightness enhancementfilm and the above described reflective layer, etc. A polarized lightreflected by the brightness enhancement film goes to the above describedreflective layer etc., and the diffusion plate installed diffusespassing light uniformly and changes the light state into depolarizationat the same time. That is, the diffusion plate returns polarized lightto natural light state. Steps are repeated where light, in theunpolarized state, i.e., natural light state, reflects throughreflective layer and the like, and again goes into brightnessenhancement film through diffusion plate toward reflective layer and thelike. Diffusion plate that returns polarized light to the natural lightstate is installed between brightness enhancement film and the abovedescribed reflective layer, and the like, in this way, and thus auniform and bright screen may be provided while maintaining brightnessof display screen, and simultaneously controlling non-uniformity ofbrightness of the display screen. By preparing such diffusion plate, itis considered that number of repetition times of reflection of a firstincident light increases with sufficient degree to provide uniform andbright display screen conjointly with diffusion function of thediffusion plate.

The suitable films are used as the above-mentioned brightnessenhancement film. Namely, multilayer thin film of a dielectricsubstance; a laminated film that has the characteristics of transmittinga linearly polarized light with a predetermined polarizing axis, and ofreflecting other light, such as the multilayer laminated film of thethin film having a different refractive-index anisotropy; an alignedfilm of cholesteric liquid-crystal polymer; a film that has thecharacteristics of reflecting a circularly polarized light with eitherleft-handed or right-handed rotation and transmitting other light, suchas a film on which the aligned cholesteric liquid crystal layer issupported; etc. may be mentioned.

Therefore, in the brightness enhancement film of a type that transmits alinearly polarized light having the above-mentioned predeterminedpolarization axis, by arranging the polarization axis of the transmittedlight and entering the light into a polarizing plate as it is, theabsorption loss by the polarizing plate is controlled and the polarizedlight can be transmitted efficiently. On the other hand, in thebrightness enhancement film of a type that transmits a circularlypolarized light as a cholesteric liquid-crystal layer, the light may beentered into a polarizer as it is, but it is desirable to enter thelight into a polarizer after changing the circularly polarized light toa linearly polarized light through a retardation plate, taking controlan absorption loss into consideration. In addition, a circularlypolarized light is convertible into a linearly polarized light using aquarter wavelength plate as the retardation plate.

A retardation plate that works as a quarter wavelength plate in a widewavelength ranges, such as a visible-light band, is obtained by a methodin which a retardation layer working as a quarter wavelength plate to apale color light with a wavelength of 550 nm is laminated with aretardation layer having other retardation characteristics, such as aretardation layer working as a half-wavelength plate. Therefore, theretardation plate located between a polarizing plate and a brightnessenhancement film may consist of one or more retardation layers.

In addition, also in a cholesteric liquid-crystal layer, a layerreflecting a circularly polarized light in a wide wavelength ranges,such as a visible-light band, may be obtained by adopting aconfiguration structure in which two or more layers with differentreflective wavelength are laminated together. Thus a transmittedcircularly polarized light in a wide wavelength range may be obtainedusing this type of cholesteric liquid-crystal layer.

Moreover, the polarizing plate may consist of multi-layered film oflaminated layers of a polarizing plate and two of more of optical layersas the above-mentioned separated type polarizing plate. Therefore, apolarizing plate may be a reflection type elliptically polarizing plateor a semi-transmission type elliptically polarizing plate, etc. in whichthe above-mentioned reflection type polarizing plate or a transflectivetype polarizing plate is combined with above described retardation platerespectively.

Although an optical film with the above described optical layerlaminated to the polarizing plate may be formed by a method in whichlaminating is separately carried out sequentially in manufacturingprocess of a liquid crystal display etc., an optical film in a form ofbeing laminated beforehand has an outstanding advantage that it hasexcellent stability in quality and assembly workability, etc., and thusmanufacturing processes ability of a liquid crystal display etc. may beraised. Proper adhesion means, such as an adhesive layer, may be usedfor laminating. On the occasion of adhesion of the above describedpolarizing plate and other optical films, the optical axis may be set asa suitable configuration angle according to the target retardationcharacteristics etc.

In the polarizing plate mentioned above and the optical film in which atleast one layer of the polarizing plate is laminated, apressure-sensitive adhesive layer may also be prepared for adhesion withother members, such as a liquid crystal cell etc. As pressure-sensitiveadhesive that forms pressure-sensitive layer is not especially limited,and, for example, acrylic type polymers; silicone type polymers;polyesters, polyurethanes, polyamides, polyethers; fluorine type andrubber type polymers may be suitably selected as a base polymer.Especially, a pressure-sensitive adhesive such as acrylics typepressure-sensitive adhesives may be preferably used, which is excellentin optical transparency, showing adhesion characteristics with moderatewettability, cohesiveness and adhesive property and has outstandingweather resistance, heat resistance, etc.

Moreover, a pressure-sensitive adhesive layer with low moistureabsorption and excellent heat resistance is desirable. This is becausethose characteristics are required in order to prevent foaming andpeeling-off phenomena by moisture absorption, in order to preventdecrease in optical characteristics and curvature of a liquid crystalcell caused by thermal expansion difference etc. and in order tomanufacture a liquid crystal display excellent in durability with highquality.

The pressure-sensitive adhesive layer may contain additives, forexample, such as natural or synthetic resins, adhesive resins, glassfibers, glass beads, metal powder, fillers comprising other inorganicpowder etc., pigments, colorants and antioxidants. Moreover, it may be apressure-sensitive adhesive layer that contains fine particle and showsoptical diffusion nature.

Proper method may be carried out to attach a pressure-sensitive adhesivelayer to one side or both sides of the optical film. As an example,about 10 to about 40 weight % of the pressure-sensitive adhesivesolution in which a base polymer or its composition is dissolved ordispersed, for example, toluene or ethyl acetate or a mixed solvent ofthese two solvents is prepared. A method in which this solution isdirectly applied on a polarizing plate top or an optical film top usingsuitable developing methods, such as flow method and coating method, ora method in which a pressure-sensitive adhesive layer is once formed ona separator, as mentioned above, and is then transferred on a polarizingplate or an optical film may be mentioned.

A pressure-sensitive adhesive layer may also be prepared on one side orboth sides of a polarizing plate or an optical film as a layer in whichpressure-sensitive adhesives with different composition or differentkind etc. are laminated together. Moreover, when pressure-sensitiveadhesive layers are prepared on both sides, pressure-sensitive adhesivelayers that have different compositions, different kinds or thickness,etc. may also be used on front side and backside of a polarizing plateor an optical film. Thickness of a pressure-sensitive adhesive layer maybe suitably determined depending on a purpose of usage or adhesivestrength, etc., and generally is 1 to 500 μm, preferably to 200 μm, andmore preferably 1 to 100 μm.

A temporary separator is attached to an exposed side of apressure-sensitive adhesive layer to prevent contamination etc., untilit is practically used. Thereby, it can be prevented that foreign mattercontacts pressure-sensitive adhesive layer in usual handling. As aseparator, without taking the above-mentioned thickness conditions intoconsideration, for example, suitable conventional sheet materials thatis coated, if necessary, with release agents, such as silicone type,long chain alkyl type, fluorine type release agents, and molybdenumsulfide may be used. As a suitable sheet material, plastics films,rubber sheets, papers, cloths, no woven fabrics, nets, foamed sheets andmetallic foils or laminated sheets thereof may be used.

In addition, in the present invention, ultraviolet absorbing propertymay be given to the above-mentioned each layer, such as a polarizer fora polarizing plate, a transparent protective film and an optical filmetc. and a pressure-sensitive adhesive layer, using a method of addingUV absorbents, such as salicylic acid ester type compounds, benzophenoltype compounds, benzotriazol type compounds, cyano acrylate typecompounds, and nickel complex salt type compounds.

A polarizing plate or an optical film of the present invention may bepreferably used for manufacturing various equipment, such as liquidcrystal display, etc. Assembling of a liquid crystal display may becarried out according to conventional methods. That is, a liquid crystaldisplay is generally manufactured by suitably assembling several partssuch as a liquid crystal cell, polarizing plates or optical films and,if necessity, lighting system, and by incorporating driving circuit. Inthe present invention, except that a polarizing plate or an optical filmby the present invention is used, there is especially no limitation touse any conventional methods. Also any liquid crystal cell of arbitrarytype, such as TN type, and STN type, π type may be used.

Suitable liquid crystal displays, such as liquid crystal display withwhich the above-mentioned polarizing plate or optical film has beenlocated at one side or both sides of the liquid crystal cell, and withwhich a backlight or a reflector is used for a lighting system may bemanufactured. In this case, the polarizing plate or optical film by thepresent invention may be installed in one side or both sides of theliquid crystal cell. When installing the polarizing plate or opticalfilms in both sides, they may be of the same type or of different type.Furthermore, in assembling a liquid crystal display, suitable parts,such as diffusion plate, anti-glare layer, antireflection film,protective plate, prism array, lens array sheet, optical diffusionplate, and backlight, may be installed in suitable position in one layeror two or more layers.

Subsequently, organic electro luminescence equipment (organic ELdisplay) will be explained. Generally, in organic EL display, atransparent electrode, an organic emitting layer and a metal electrodeare laminated on a transparent substrate in an order configuring anilluminant (organic electro luminescence illuminant). Here, an organicemitting layer is a laminated material of various organic thin films,and much compositions with various combination are known, for example, alaminated material of hole injection layer comprising triphenylaminederivatives etc., a luminescence layer comprising fluorescent organicsolids, such as anthracene; a laminated material of electronic injectionlayer comprising such a luminescence layer and perylene derivatives,etc.; laminated material of these hole injection layers, luminescencelayer, and electronic injection layer etc.

An organic EL display emits light based on a principle that positivehole and electron are injected into an organic emitting layer byimpressing voltage between a transparent electrode and a metalelectrode, the energy produced by recombination of these positive holesand electrons excites fluorescent substance, and subsequently light isemitted when excited fluorescent substance returns to ground state. Amechanism called recombination which takes place in a intermediateprocess is the same as a mechanism in common diodes, and, as isexpected, there is a strong non-linear relationship between electriccurrent and luminescence strength accompanied by rectification nature toapplied voltage.

In an organic EL display, in order to take out luminescence in anorganic emitting layer, at least one electrode must be transparent. Thetransparent electrode usually formed with transparent electricconductor, such as indium tin oxide (ITO), is used as an anode. On theother hand, in order to make electronic injection easier and to increaseluminescence efficiency, it is important that a substance with smallwork function is used for cathode, and metal electrodes, such as Mg—Agand Al—Li, are usually used.

In organic EL display of such a configuration, an organic emitting layeris formed by a very thin film about 10 nm in thickness. For this reason,light is transmitted nearly completely through organic emitting layer asthrough transparent electrode. Consequently, since the light thatenters, when light is not emitted, as incident light from a surface of atransparent substrate and is transmitted through a transparent electrodeand an organic emitting layer and then is reflected by a metalelectrode, appears in front surface side of the transparent substrateagain, a display side of the organic EL display looks like mirror ifviewed from outside.

In an organic EL display containing an organic electro luminescenceilluminant equipped with a transparent electrode on a surface side of anorganic emitting layer that emits light by impression of voltage, and atthe same time equipped with a metal electrode on a back side of organicemitting layer, a retardation plate may be installed between thesetransparent electrodes and a polarizing plate, while preparing thepolarizing plate on the surface side of the transparent electrode.

Since the retardation plate and the polarizing plate have functionpolarizing the light that has entered as incident light from outside andhas been reflected by the metal electrode, they have an effect of makingthe mirror surface of metal electrode not visible from outside by thepolarization action. If a retardation plate is configured with a quarterwavelength plate and the angle between the two polarization directionsof the polarizing plate and the retardation plate is adjusted to π/4,the mirror surface of the metal electrode may be completely covered.

This means that only linearly polarized light component of the externallight that enters as incident light into this organic EL display istransmitted with the work of polarizing plate. This linearly polarizedlight generally gives an elliptically polarized light by the retardationplate, and especially the retardation plate is a quarter wavelengthplate, and moreover when the angle between the two polarizationdirections of the polarizing plate and the retardation plate is adjustedto π/4, it gives a circularly polarized light.

This circularly polarized light is transmitted through the transparentsubstrate, the transparent electrode and the organic thin film, and isreflected by the metal electrode, and then is transmitted through theorganic thin film, the transparent electrode and the transparentsubstrate again, and is turned into a linearly polarized light againwith the retardation plate. And since this linearly polarized light liesat right angles to the polarization direction of the polarizing plate,it cannot be transmitted through the polarizing plate. As the result,mirror surface of the metal electrode may be completely covered.

EXAMPLES

Description will be given of a construction and effect of the inventionwith examples and the like showing them below. Note that in theexamples, part or parts and % are based on weight unless otherwisespecified.

(Viscosity of Aqueous Adhesive Solution)

The prepared aqueous adhesive solution (room temperature: 23° C.) wasmeasured with a rheometer (RSI-HS, manufactured by Haake).

(Average Particle Size of Colloid)

An aqueous colloidal alumina solution was measured with a particle sizedistribution meter (Nanotrac UPA150, manufactured by Nikkiso Co., Ltd.)by dynamic light scattering (optical correlation technique). Samplesother than an aqueous colloidal silica solution were measured by thesame method. The aqueous colloidal silica solution was measured withanother particle size distribution meter (ELS-8000, manufactured byOtsuka Electronics Co., Ltd.) by dynamic light scattering (opticalcorrelation technique).

Example 1 Polarizer

A 75 μm-thick polyvinyl alcohol film with an average degree ofpolymerization of 2400 and a saponification degree of 99.9% by mole wasimmersed and allowed to swell in warm water at 30° C. for 60 seconds.The film was then immersed in an aqueous solution of iodine/potassiumiodide (0.5/8 in weight ratio) at a concentration of 0.3%, whilestretched to a stretch ratio of 3.5 times, so that the film was dyed.The film was then stretched in an aqueous borate ester solution at 65°C. such that the total stretch ratio reached 6 times. After thestretching, the film was dried in an oven at 40° C. for 3 minutes,resulting in a polarizer.

(Transparent Protective Film)

A 40 μm-thick triacetylcellulose film was used as a transparentprotective film.

(Preparation of Adhesive)

At a temperature of 30° C., 100 parts of a polyvinyl alcohol-based resinhaving an acetoacetyl group (1200 in average degree of polymerization,98.5% by mole in degree of saponification, 5% by mole in degree ofacetoacetylation) and 50 parts of methylolmelamine were dissolved inpure water to form an aqueous solution with a controlled solidconcentration of 3.7%. Eighteen parts of an aqueous colloidal aluminasolution (15 nm in average particle size, 10% in solid concentration,positively charged) was added to 100 parts of the above aqueous solutionto form an aqueous adhesive solution. The aqueous adhesive solution hada viscosity of 9.6 mPa·s and a pH in the range of 4 to 4.5.

(Preparation of Polarizing Plate)

The adhesive was applied to one side of the transparent protective filmso as to form an adhesive layer with a thickness of 80 nm after drying.The adhesive was applied at a temperature of 23° C., 30 minutes afterits preparation. At a temperature of 23° C., the adhesive-coatedtriacetyl cellulose film was then laminated to both sides of thepolarizer with a roller machine, and then the laminate was dried at 55°C. for 6 minutes to give a polarizing plate.

Examples 2 to 15 and Comparative Examples 1 to 4

Adhesives were prepared using the process of Example 1, except that thetype of each component and the content of each component used werechanged as shown in Table 1. Polarizing plates were also prepared usingthe resulting adhesives in the same manner as Example 1.

(Evaluations)

The polarizing plates obtained in the examples and the comparativeexamples were evaluated as described below.

(Adhesion)

At an end of the polarizing plate, the cutting edge of a cutter wasinserted between the polarizer and the transparent protective film. Atthe insertion site, the polarizer and the transparent protective filmwere held and pulled in opposite directions, respectively. At that time,when the polarizer and/or the transparent protective film was broken sothat they could not be separated from each other, their adhesion wasdetermined as good (marked by “◯”). In contrast, when the polarizer andthe transparent protective film were partially or entirely separatedfrom each other, their adhesion was determined as poor (marked by “x”).

(Amount of Peeling)

The polarizing plate was cut 50 mm long in the direction of theabsorption axis of the polarizer and 25 mm long in the directionperpendicular to the absorption axis so that a sample was prepared.While the sample was immersed in hot water at 60° C., the amount (mm) ofthe peeling edge of the sample was measured over time. The amount (mm)of the peeling was measured with a vernier caliper. The amount (mm) ofthe peeling after 5 hours is shown in Table 1.

(Appearance Evaluation: Knick Defects)

The polarizing plate was cut in a size of 1000 mm×1000 mm to form asample. The polarizing plate sample was placed under a fluorescent lamp.Another polarizing plate was placed on the light source side of thepolarizing plate sample such that their absorption axes wereperpendicular to each other, and in this configuration, light leakageportions (knick defects) were counted.

(Optical Properties)

A sample 50 mm×25 mm in size was obtained by cutting a widthwise centerportion of the resulting polarizing plate in such a manner that the longside of the sample made an angle of 45° with the absorption axis of thepolarizing plate. The sample was measured for single-substancetransmittance (%) and degree of polarization with an integrating spheretype spectral transmittance meter (DOT-3C, manufactured by MurakamiColor Research Laboratory).

TABLE 1 Polyvinyl Colloidal Metal Compound Alcohol-Based ResinCrosslinking Agent Average Amount Amount particle Amount Type (Parts)Type (Parts) Type size (nm) Charge (Parts) Example 1 AA-Modified 100Methylolmelamine 50 Alumina 15 Positive 75 Example 2 AA-Modified 100Methylolmelamine 50 Alumina 75 Positive 75 Example 3 AA-Modified 100Methylolmelamine 30 Alumina 15 Positive 140 Example 4 AA-Modified 100Methylolmelamine 30 Alumina 15 Positive 30 Example 5 Completely 100Methylolmelamine 50 Alumina 15 Positive 75 Saponified Example 6AA-Modified 100 Methylolmelamine 50 Silica 20 Negative 50 Example 7AA-Modified 100 Methylolmelamine 50 Zirconia 20 Positive 50 Example 8AA-Modified 100 Methylolmelamine 50 Titania 15 Positive 50 Example 9AA-Modified 100 Methylolmelamine 50 Tin 15 Positive 50 Oxide Example 10AA-Modified 100 Glyoxal 50 Alumina 75 Positive 75 Example 11 AA-Modified100 Glutaraldehyde 50 Alumina 15 Positive 75 Example 12 AA-Modified 100Epoxy Compound 50 Alumina 15 Positive 75 Example 13 AA-Modified 100Silane Coupling 50 Alumina 15 Positive 75 Agent Example 14 AA-Modified100 Titanium 50 Alumina 15 Positive 75 Coupling Agent Example 15AA-Modified 100 Methylolmelamine 5 Alumina 15 Positive 75 ComparativeAA-Modified 100 Methylolmelamine 50 — — — — Example 1 ComparativeAA-Modified 100 Methylolmelamine 50 Alumina 1 μm Positive 75 Example 2Comparative AA-Modified 100 Methylolmelamine 50 Alumina 75 Positive 300Example 3 Comparative Completely 100 Methylolmelamine 50 — — — — Example4 Saponified Viscosity of Adhesive Solution (mPa · s) ThicknessEvaluations Solid of Peeling Knick Concentration Viscosity AdhesiveAmount Defects Single-Substance Polarization (Wt %) (mPa · s) Layer (mm)Adhesion (mm) (Counts) Transmittance Degree Example 1 5.55 9.6 70 ◯ <1 043.8 99.9 Example 2 5.55 8.1 80 ◯ <1 1 43.7 99.9 Example 3 6.24 10.2 100◯ 1 0 43.7 99.9 Example 4 4.55 10.3 60 ◯ 1 1 43.8 99.9 Example 5 5.5512.1 90 ◯ 10 0 43.8 99.9 Example 6 5.45 9.5 60 ◯ 1 5 43.6 99.9 Example 75.45 8.1 80 ◯ 1 3 43.6 99.9 Example 8 5.45 8.5 90 ◯ 1 4 43.7 99.9Example 9 5.45 7.5 90 ◯ 2 3 43.5 99.9 Example 10 5.55 9.3 80 ◯ 8 1 43.399.9 Example 11 5.55 9.7 80 ◯ 9 0 43.7 99.9 Example 12 5.55 8.9 70 ◯ 8 043.5 99.9 Example 13 5.55 10.2 70 ◯ 11 1 43.5 99.9 Example 14 5.55 10.360 ◯ 8 0 43.7 99.9 Example 15 5.10 10.5 80 ◯ 10 1 43.3 99.9 Comparative3.7 7.0 30 ◯ <1 24 43.8 99.9 Example 1 Comparative 5.55 8.2 2 μm ◯ 1 443.8 97.9 Example 2 Comparative 8.4 4.8 120 X 5 0 43.7 99.9 Example 3Comparative 3.7 7.9 60 ◯ 11 7 43.7 99.9 Example 4

In Table 1, “AA-modified” means a polyvinyl alcohol-based resin havingan acetoacetyl group. Concerning the crosslinking agents used, the epoxycompound was EX201 manufactured by Nagase ChemteX Corporation, thesilane coupling agent was KBM-903 manufactured by Shin-Etsu ChemicalCo., Ltd., and the titanium coupling agent was TC-300 manufactured byMatsumoto Chemical Industry Co., Ltd. Concerning the colloidal metalcompounds used, the colloidal alumina with an average particle size of15 nm was Alumina Sol 10A manufactured by Kawaken Fine Chemicals Co.,Ltd., the colloidal alumina with an average particle size of 75 nm was a75 nm particle size product of alumina sol manufactured by Kawaken FineChemicals Co., Ltd., the colloidal alumina with an average particle sizeof 1 μm was a 1 μm particle size product of alumina sol manufactured byKawaken Fine Chemicals Co., Ltd., the colloidal silica was ZR-30ALmanufactured by Nissan Chemical Industries, Ltd., the colloidal titaniawas PW1010 manufactured by Catalysts & Chemicals Industries Co., Ltd.,and the colloidal tin oxide was C-10 manufactured by Taki Chemical Co.,Ltd. The amount of the colloidal metal compound means the amount of thesolid (converted value) added to 100 parts by weight of the polyvinylalcohol-based resin. The pH of all the aqueous adhesive solutions was inthe range of 4 to 4.5. The solid concentration of the adhesive solutionmeans the content of the polyvinyl alcohol-based resin, the crosslinkingagent and the colloidal metal compound in the adhesive solution.

Table 1 shows that the polarizing plates of the examples have goodadhesion and are prevented from generating knicks. It is apparent thatthe occurrence of knicks is prevented particularly in Examples 1 to 4and 10 to 15 using alumina for the colloidal metal compound. It is alsoapparent that Examples 1 to 4 each using a polyvinyl alcohol-based resinhaving an acetoacetyl group provides good water resistance and goodadhesion and prevent the occurrence of knicks. The occurrence of knicksis not prevented in Comparative Examples 1 and 4 using no colloidalmetal compound. In Comparative Example 2, the average particle size ofthe colloidal metal compound is relatively large and thus affects theoptical properties and reduces the degree of polarization. InComparative Example 3, the amount ratio of the colloidal metal compoundis so large that the adhesion is not satisfactory.

What is claimed is:
 1. A polarizing plate, comprising: a polarizer; anda transparent protective film provided on at least one side of thepolarizer with an adhesive layer interposed therebetween, wherein theadhesive layer comprises: a resin solution comprising a polyvinylalcohol-based resin, a crosslinking agent and a colloidal metal compoundwith an average particle size of 1 nm to 100 nm, wherein 200 parts byweight or less of the colloidal metal compound is added to 100 parts byweight of the polyvinyl alcohol-based resin; and wherein the colloidalmetal compound is at least one selected from the group consisting ofcolloidal alumina, colloidal silica, colloidal zirconia, colloidaltitania, and colloidal tin oxide.
 2. The polarizing plate according toclaim 1, wherein the colloidal metal compound has a positive charge. 3.The polarizing plate according to claim 2, wherein the colloidal metalcompound is colloidal alumina.
 4. The polarizing plate according toclaim 1, wherein the polyvinyl alcohol-based resin is a polyvinylalcohol-based resin having an acetoacetyl group.
 5. The polarizing plateaccording to claim 1, wherein the crosslinking agent contains a methylolgroup-containing compound.
 6. The polarizing plate according to claim 1,wherein an amount of the crosslinking agent is of 4 to 60 parts byweight based on 100 parts by weight of the polyvinyl alcohol-basedresin.
 7. The polarizing plate according to claim 1, wherein theadhesive layer has a thickness of 10 nm to 300 nm, and the thickness ofthe adhesive layer is larger than the average particle size of thecolloidal metal compound contained in the adhesive for polarizing plate.8. An optical film, comprising a laminate including the polarizing plateaccording to claim
 1. 9. An image display, comprising the optical filmaccording to claim
 8. 10. An image display, comprising the polarizingplate according to claim
 1. 11. The polarizing plate according to claim1, wherein the concentration of the resin solution is 0.1 to 15% byweight.